The petroleum well is a hostile environment, as high pressure and temperature, fluid composition and movement together render measurement while drilling (MWD) and/or logging while drilling (LWD) operations challenging. The equipment used for MWD and LWD operations include various electronics that may be subjected to temperatures above about 125 degrees Celsius. Because the lifespan and reliability of printed circuit boards at these temperatures can be adversely affected, ceramic-substrate technologies have been developed using substrates such as thick film ceramics, high temperature co-fired substrates and low temperature co-fired substrates.
In many electrical components using ceramic substrates, aluminum wirebond connections are used to interconnect bare dies with a substrate having a thick (greater than about 1 micron) plating layer. In some cases, the plating layer may be a gold layer. In these cases, the interconnection between the gold layer and the aluminum wirebond may have limited reliability at high temperature above about 125 degrees Celsius. Poor reliability can result from formation of intermetallic compounds such as Au5Al2 (sometimes known as white plague) and AuAl2 (sometimes known as purple plague) that can form between the gold layer and the aluminum wirebond. These compounds can increase electrical resistance and weaken the connection between the aluminum wirebond and the gold layer.